The present invention relates to a resin composition rich in heat resistance, oil resistance, and thermal aging resistance and excellent in tensile elongation characteristics. More particularly, the invention relates to a thermoplastic resin composition which comprises a styrene resin or poly(phenylene ether) resin, an olefin resin, and a partially hydrogenated block copolymer having a specific structure and is suitable for containers for foods, etc.
Styrene resins are extensively used as injection molding materials or sheet-forming materials because they have satisfactory processability and excellent mechanical properties. However, since styrene resins have poor oil resistance and suffer an abrupt decrease in physical property upon contact with oils such as margarine and sesame oil, they have been used in limited applications. It has hence been attempted to mix an olefin resin therewith in order to improve the oil resistance. However, styrene resins have poor compatibility with olefin resins and, hence, the blending necessarily gives a composition which undergoes a separation phenomenon and is brittle.
On the other hand, poly(phenylene ether) resins are excellent in mechanical properties, electrical properties, etc. and are extensively used in applications such as the housings of business machines or apparatus, various industrial parts, and the like. However, these resins are poor in oil resistance and impact resistance and attempts are being made to mix an olefin resin therewith in order to improve these properties. However, the two kinds of resins are poorly compatible with each other, resulting in a separation phenomenon.
For overcoming those problems, various compositions containing a block copolymer added thereto have been proposed. For example, Japanese Patent Laid-Open No. 38338/1981 proposes a composition comprising a polyolefin resin and a polystyrene resin and containing a hydrogenated block copolymer obtained by hydrogenating a block copolymer having at least one vinylaromatic compound polymer block A and at least one conjugated diene polymer block B to such a degree that at least 70% of the double bonds in the block copolymer are saturated. Specifically, the hydrogenated block copolymers disclosed therein include, for example, one obtained by hydrogenating an A-B type block copolymer having a combined styrene content of 50% and a vinyl content before hydrogenation of 13% so as to hydrogenate 92% of the double bonds. In Japanese Patent Laid-Open No. 174550/1989 also is proposed a composition comprising a polyolefin resin and a polystyrene resin and containing a similar hydrogenated block copolymer. Specifically, the hydrogenated block copolymers disclosed therein include, for example, one obtained by hydrogenating an A-B type block copolymer having a combined styrene content of 35% and a vinyl content in isoprene before hydrogenation of 8% so as to hydrogenate 93% of the double bonds. However, the hydrogenated block copolymers used in these compositions are ones having a high degree of hydrogenation and have had a problem that their productivity is low. For example, the hydrogenation period necessary for obtaining the hydrogenated block copolymer disclosed in Japanese Patent Laid-Open No. 38338/1981 is 6 hours, while the hydrogenation period necessary for obtaining the hydrogenated block copolymer disclosed in Japanese Patent Laid-Open No. 174550/1989 is 8 hours. Namely, considerable time has been required. There has hence been a desire for a polymer which is a block copolymer easy to produce with satisfactory productivity and has excellent properties when added to a composition comprising a polyolefin resin and a polystyrene resin. In addition, the compositions disclosed in those references are insufficient in tensile elongation characteristics although they have been improved in compatibility between the polyolefin resin and polystyrene resin. A further improvement is hence desired.
Furthermore, Japanese Patent Laid-Open No. 12800/1997 proposes a composition comprising a polypropylene resin and poly(phenylene ether) and containing a hydrogenated block copolymer obtained by hydrogenating to from 65 to 80% a block copolymer having a vinylaromatic compound polymer block A and a conjugated diene polymer block B having a large vinyl bond amount. Specifically, the hydrogenated block copolymers disclosed therein include, for example, one obtained by hydrogenating an A-B type block copolymer having a combined styrene content of 60% and a vinyl content before hydrogenation of 74% so as to hydrogenate 68% of the double bonds. However, since the hydrogenated block copolymer used here contains a conjugated diene polymer having a large vinyl amount, the composition has had a drawback that it has poor resistance to thermal aging at high temperatures.
An object of the invention is to provide a thermoplastic resin composition rich in heat resistance, oil resistance, and thermal aging resistance and excellent in tensile elongation characteristics by adding a partially hydrogenated block copolymer having a specific structure to a styrene resin and/or poly(phenylene ether) resin and an olefin resin.
The present inventors made intensive investigations in order to obtain a block copolymer which, when used in blending a styrene resin or poly(phenylene ether) resin with an olefin resin, gives a resin composition rich in heat resistance, oil resistance, and thermal aging resistance and excellent in tensile elongation characteristics and which has satisfactory productivity. As a result, it has been found that the aim can be accomplished by adding a partially hydrogenated block copolymer having a specific structure to a styrene resin and/or poly(phenylene ether) resin and an olefin resin. The invention has thus been completed.
Namely, the invention relates to a resin composition which comprises (A) from 95 to 5% by weight of styrene resin and/or poly(phenylene ether) resin, (B) from 5 to 95% by weight of olefin resin, and (C) a partially hydrogenated block copolymer in an amount of from 2 to 30 parts by weight per 100 parts by weight of the sum of ingredients (A) and (B), wherein (C) is a partially hydrogenated block copolymer obtained by hydrogenating a block copolymer which has at least one polymer block X mainly comprising a vinylaromatic compound and at least one polymer block Y mainly comprising a conjugated diene compound and has a combined vinylaromatic compound content of from 30 to 80% by weight and in which the vinyl bond amount in the conjugated dienes before hydrogenation is from 20% by weight to less than 65% by weight to thereby saturate from 35% to less than 70% of the double bonds derived from the conjugated diene compounds in the block copolymer.